German patent document No. 35 45 547 discloses a ball cock in which the valve seat is received in a pressurizable housing shell which has an overall length substantially equal to that of the valve seat so that, when the pipe-connecting elements are affixed to the ends of the housing, the resilient and deformable seals are braced directly by the pipe-connecting elements against the seat. The pipe-connecting elements can have flanges which are connected across the length of the housing, outwardly of the latter, by tie bolts.
The elasticity of the seals provide resilient bias of the seat rings against the valve ball. The ceramic wear parts of the valve do not bear the force of pressure within the valve, the force being borne by the surrounding pressurizable housing shell. Thus the radially effective operating pressure, the bending moments of axially effective tension forces applied by the pipeline to the valve are all taken up directly by the housing.
This construction has been very successful. However, problems are encountered when the valve ball is intended to function as a throttle for abrasive fluids containing solid particles
An increase in the flow velocity in the region of any throttling gap with the valve ball in a partially closed state, together with a strong turbulence in the flow path downstream of the throttle opening gives rise to a rapid wear in the region of the pipe-connecting elements, in the region of the adjacent pipes of the pipeline and in the region of the resilient seal since these elements have no effective wear protection.